The distinction of peripheral primitive neuroectodermal tumors (PNET) from other tumors of neuroectodermal origin, such as neuroblastoma and central PNET, or even rhabdomyosarcoma is not always easy. Although a specific cytogenetic abnormality, t(11;22) (q24;q12), characterizes peripheral PNET, it is not always feasible to perform cytogenetic analysis for diagnostic purposes. The recent identification of transcribed sequences from the breakpoint regions and the detection of abnormal hybrid transcripts in those cases with the translocation has led to the use of RT-PCR as a sensitive diagnostic method to demonstrate specific fusion transcripts in those tumors with t(ll;22) . We have employed the RT-PCR technique to detect abnormal transcripts in a number of pediatric solid tumors and cell lines. Our preliminary data have shown specific expression of abnormal transcripts only by the peripheral PNET and not central PNET or neuroblastomas. The specificity of the method will be tested on a larger number of tumors.